Method for firing explosives



Dec. 10, 1929.

L: M. MCBRIDE 1,738,595

uswaon FOR name EXPLOSIVES Filed may 1'7. 1927 10 OHMS RESISTANCE 5 OHMS'RESISTANCE 5 O0 20 CAPS W OHMS RESISTANCE 5 0-O-Q- 3O CAPS W omns RESISTANCE 5 OO-O-Q- 4O CAPS -O0OO-- 5'0 OHMS RESISTANCE 5 OO-O-O-O 5O CAPS 1o(1+N') OHMS RESISTANCE 5 M/VENTOR 'N'CAPS -o-o-o-o-o a'' Lew/ls M Br/b/e ATTORNEYS.

. 40 or fuse heads, in a firing Patented Dec. 10, 1929 UNITED STATES PATENTL OFFICE LEWIS I. MCBRIDE, OF BOSTON, MASSACHUSETTS, ASSIGNOR TO HEBQULES POWDER COMPANY, A. CORPORATION. OF DELAWARE Y METHOD FOR FIRING EXPLOSIVES Application filed Kay 17, 1927. Se uaI No. 191,999.

My invention relates to a method for firing explosives and more particularly to a method for firing blasting charges, though as will appear hereinafter, my invention is adaptable to a wide field of use including the firing of guns.

Heretofore in the commercial use of explosives, as in blasting for one purpose or another, it has been customary to fire the charges electrically, through the medium of a firing element as, for example, a detonating cap or a fuse head, the caps or fuse heads for a number of charges being connected to an electric firing circuit in parallel, in series or in series parallel. The customary met ods of electric firing have served well enoufigh where only a small number of charges are red, but where it is desired to fire any lar e number of charges, the customary met ods are impractical because of the high current values required to overcome the sum of the resistances of the firing elements necessary to fire the desired number of charges and which may easily exceed the capacity of the usual blasting machines. Thus, present methods of electrical firing limit the num-- ber of charges which may be fired on one circuit.

Now, it is the object of my invention to y a very large number of charges may be fired with a minimum amount of electrical energy and whereby the number of charges capable of being fired on a single circuit and within the capacity of the ordinary blasting machine will be greatly increased.

According to the method embodying my invention broadly, I arrange a plurality of electric firing elements, as detonating caps circuit and provide differential resistance to the flow of a current to the different firing elements so that when electric energy, as an electric current, is imparted to the firing circuit, the current, taking the path of least resistance, will'actuate the firing elements connected to the circuit through the least resistance and will subsequently actuate the firing elements connected to the circuit through greater resistance. Thus, it will be observed that in carrying rovide a method of firing explosives where out my method, the current requirement is defined by that necessary to overcome the maximum resistance used in connecting the firing elements in the circuit, ratherthan by the sum of the resistances of the firing elements.

More specifically, in accordance with my invention, I arrange in parallel in an electric firing circuit a plurality of series of firing elements and provide a differential resistance in different series; and still more specifically, I arrange in parallel in a firing circuit a plurality of firing elements in series of varying resistance.

In putting into practice the method embodying my invention, a plurality of series of firing elements, as, for example, detonat ing caps, each associated with an explosive charge, may be connected in parallel in an electric firing circuit and differential resistance between two or more series obtained by providing in two or more series a different number of firing elements, since the resist- .ance in each series is equal to the sum of the resistances of the several firing elements in each series.

Referring now to the accompanying drawing, in whichthe figure is a diagrammatic illustration of an electric firing circuit with a plurality of series of explosive charges to be red by the method embodying my invention, w indicates any convenient source of electric energy, which may be a power line, generator, or ordinary blasting machine and. which may be a source of either alternating or direct current. y and 2 respectively, indicate leads connected to the source of electric energy. a,'a a a a and a indicate a plurality of graded series of electric firing elements, the several series being connected across the leads y, z,by means of wire b. The several series a to a comprise, respectively graded series of resistances obtained, in the circuit illustrated, by the provision of varying numbers of firing elements in each series.

The variation of the number of firing elements, in order to obtain the desired graded series of resistances, may be made according to any suitable and desirable method, such as an arithmetical or geometricalprogression; 109

or it may be based upon some value of a, which varies either directly or inversely as some constant; upon a percentage basis of a, or by any other suitable system.

As each of the firing elements indicated in the series a to a inclusive, have the same or a proportionate resistance and are separated and isolated in the same manner under the same conditions, then theheat required to fuse the bridge wire, or other element of each firing element is the same.

With a given voltage E, across the firing circuit formed by the conductors 3 and z, a current flowing through the several series a to a inclusive, varies inversely with the resistance R of those circuits.

Assuming that the number of firing elements, and consequently the resistance, is varied in an arithmetical progression whereby each term is obtained from the preceding term by adding a constant difference (Z having for instance a resistance of ten ohms; a being for example a series of firing elements having a total'resistance of ten ohms, then a =a+d; a =a+2d; a =a+3d; a =a+4d; a =a+nd; or otherwise stated, the resistance of a is equal to 10 ohms; of 0. to 20; of a to 30; of a to 40, of a, to and of a to 10 (1+n) ohms, respectively. It will be seen from the foregoing proportions that the circuit a having one-half of the resistance of a passes twice as much current. However, as the heating effect varies as the square of the current there is produced four times as much heat in each firing element, inasmuch as the resistance R of each, is the same. In a like manner the heat generated in the firing elements in the circuit a is nine times that in the circuit a sixteen times that in the circuit a twenty-five times that in the circuit a, and (n+ 1) 2 times that in the circuit 0,

The time required to actuate a firing element varies inversely as the square of the current, therefore doubling the current, as in the case of series a over series (1 the time of firing the series a is four times faster than series a It will be seen from the above that with a I suitable value of voltage impressed across the that particular circuit is ruptured and opened,

firing circuit that current will flow through the several graded series circuits a to a inclusive, with values inversely proportional to their individual resistances and that the resultant heating effect in the .individual firing elements of those circuits will vary as the square of the current values therein. Consequently the graded series of connected firing elements are actuated in a regular turn of order from the series of lowest resistance progressively through those of succeeding higher resistance.

As each series of firing elements is actuated,

and the load on the source of current is reduced by the amount of current which was flowing in that series. The initial load will therefore progressively diminish as the series circuits open successively. This progressive diminishing or reduction of the current tends to cause a correspondingly successive increase or rise in the voltage of the system thereby increasing the current in the rc maining series circuits and further augmenting the heating effect and the actuation of the successive series.

By this method of connection and firing, it is apparent that the capacity of the source of current need not be such as would be reuired to fire the entire number of connected ring elements instantaneously or simultaneously, and by this arrangement of circuits a greater number of charges can be fired with a given energy value of electricity, therefore the size and weight of a firing mechanism for firing any given number of charges can be materially reduced.

It will be understood that in accordance with my invention, the resistances of the several series a to a may be varied by any convenient means other than by the use of varying numbers of firing elements in theseveral series, as described; and further, that the several series need not be respectively of different resistance, it being only necessary, depending upon the number of charges to be fired, that two or more series be of different resistance.

It will be understood that I do not intend that my invention shall be limited to the firing of commercial explosives, nor to the use of any particular type of firing element, since it is adaptable to other uses, as for example, the firing of guns and may be used with any form of electrically operated firing element, as for example, a detonating cap or fuse head, whether such acts directly or in directly to fire the explosive charge.

Having now fully described my invention, what I claim and desire to protectby Letters Patent is 1. The method of firing explosives, which comprises arranging in parallel in an electric-firing circuit a plurality of series of explosive charge firing elements, providing differential resistance to the flow of current in diflt'erent series by variation in the number of firing elements in different series and imparting electrical energy to the firing circuit.

2. The method of firing explosives, which comprises arranging in parallel in an electric firing circuit a lurality of series of explosive charge firing e ements, providing a differential resistance to the flow of current in a plurality of such series by providing a different number of firing elements in one series from that in another series and imparting electrical energy to the firing circuit.

3. The method of firing explosives, which comprises arranging in parallel in an electric firing circuit a plurality of series of explosive charge firing elements,

providing a differential resistance to the flow of'current in such series by providing a, difi'erent number of fir ing elements in each series and imparting electrical energy to the firing circuit.

In testimony of which invention, I have hereunto set my hand, this 10th day of Ma at Boston, Mass, on

IS M. MoBRIDE. 

